The invention concerns a method for transmission of time-critical packets.
A transition from analog to digital transmission systems is now occurring in television technology. A source code method, operating according to the MPEG standard, is known in conjunction with digital transmission systems. This permits data compression, which allows particularly efficient data transmission. For example, it was possible in analog technology to transmit a television program on a satellite transponder with 33 MHz bandwidth. On the other hand, five to ten programs of the same quality can be transmitted on the same transponder with digital technology.
In the MPEG standard, the individual programs are transmitted in time multiplex in the form of data streams, which are divided into blocks or data packets. A program consists of several data streams of different type (video information, audio information, auxiliary information), the so-called elementary data streams. The elementary data streams of a program are combined in a program multiplexer to a program data stream. Several program data streams are assembled in a transport multiplexer to a transport data stream. This is transmitted to a satellite via a so-called uplink, which converts the signal and distributes it for satellite direct reception at the viewer.
The MPEG data stream is regenerated from the signals received by a satellite antenna by means of a satellite receiver or a set top box and fed to a television or video recorder connected downline. Separation of data packets pertaining to a desired television program and MPEG decoding occur there. The data packets pertaining to the desired television program are transmitted in time multiplex with data packets allocated to other programs and are therefore spaced from each other in time. In each of the data packets that are assigned to the desired program, data are contained that give information about the time of transmission of the next data packet that pertains to the desired program. This information concerning the time of transmission of the next data packet is used by the MPEG decoder to set a time window, in which the appearance of this next data packet that must be subjected to MPEG decoding is waited for. Consequently, data packets that do not belong to the desired program need not be checked and temporarily stored in the MPEG decoder. The storage capacity of the memory in the MPEG decoder must consequently be only large enough so that a complete data packet can be decoded. During transmission of MPEG-coded data packets, time-critical data packets are therefore involved, whose relative time position with respect to each other must be known during MPEG decoding.
This information concerning the time position of individual data packets of a desired radio program relative to each other, however, is lost if MPEG-coded signals are to be transmitted, for example, via a radio transmission link whose transmission bandwidth is much smaller than the bandwidth available for satellite transmission of MPEG-coded signals. Both the latency and travel time of data packets are not predictable in wireless radio transmission systems, since they are dependent on the system occupation (CSMA access) and on the transmission distance.
Starting from this prior art, the underlying task of the invention is to provide a new way, with which time-critical data packets can be transmitted over a travel time-burdened transmission link.